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Prior Authorization Required*
*If prior authorization is not submitted, test may be delayed.
Test Overview
Test Methodology

This fragile X test uses a polymerase chain reaction (PCR) optimized for GC-rich region and capillary electrophoresis to detect the number of cytosine-guanine-guanine (CGG) repeats in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene by incorporating a gene-specific primer pair that amplifies the entire CGG repeat region, and a primer that randomly anneals inside and amplifies the CGG repeat region in generating fragments of different sizes (CGG primed “shoulder” peaks).

If needed, methylation PCR and capillary electrophoresis are performed to determine the methylation status of the FMR1 gene for a patient with a premutation or a full mutation CGG repeat expansion; or for a female patient with only one reported allele size, except for when the presence of two X chromosomes are indicated by two different AGG interruption patterns in the CGG primed peaks, or the sex chromosome status is known from a previous genetic test result (e.g., microarray or karyotype).

Test Usage

Analysis of CGG repeats present in the FMR1 gene in a patient with clinical features consistent with Fragile X Syndrome or determination of the carrier status of a family member.

Reference Range *

Normal alleles: 5-44 CGG repeats; Intermediate (gray zone) mutations: 45-54 CGG repeats; Premutations: 55-200 CGG repeats; Full Mutation: >200 CGG repeats. Interpretative report provided.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Limitations

This assay can detect up to 200 CGG repeats in the FMR1 gene. Samples containing > 200 CGG repeats will be reported as "full mutation (>200 CGG repeats)".

Test Details
Days Set Up
Monday - Thursday
Analytic Time

21 days

Soft Order Code
MiChart Code
Fragile X DNA Analysis (MMGL)
  • Fragile X Frag Analysis Shadow
  • Fragile X Mutation Detection by Fragment Analysis
  • FXPB
  • Fragile X Synd Car Det,Blood
  • Fragile X Syndrome
  • x-linked mental retardation
  • Fragile X tremor ataxia syndrome
  • Fragile X associated premature ovarian insufficiency (FXPOI)
  • Autism / Intellectual Disability
MMGL Molecular Genetics
Specimen Requirements
Collection Instructions

Collect specimen in a lavender top tube. Send intact specimen within 24 hours if stored at room temperature or within 5 days if stored refrigerated. Include the patient's family history, pedigree, and ethnicity on the test requisition. Obtaining informed consent from the patient prior to genetic testing is strongly recommended. If desired, a UMHS Request and Consent for Genetic Testing form can be obtained from the MMGL Molecular Genetics Laboratory by contacting the MLabs Client Services Center at 800-862-7284 or online at

Normal Volume
5 - 10 mL EDTA whole blood
Minimum Volume
2 mL EDTA whole blood
Additional Information

The American College of Medical Genetics recommends that both a routine karotype (Chromosome Analysis, Blood, Constitutional) AND a molecular test (Fragile X Syndrome Mutation Detection) be performed. By ordering this test the clinician acknowledges that informed consent has been obtained from the patient as required by applicable state or federal laws and the ordering clinician has authorization from the patient permitting MLabs to report the test results to the ordering clinician. Test includes medical geneticist interpretation of results billed as a separate additional charge. This test is not available without interpretation.

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